1. Field of the Invention
The present invention relates to epoxy guns and, more particularly, to hand-operated epoxy guns of the type employing dual component cartridges and dual ejector pistons for dispensing two component materials.
2. Description of the Background
There are a wide variety of dispensing guns that are used to dispense many types of fluid compositions such as urethane, vinyl, polyester, epoxy and other plastics. Conventional dispensing guns are constructed to provide a barrel to receive a cartridge containing fluid compound which has a dispensing nozzle at one end. These dispensing guns typically have a plunger shaft that is driven by a manual trigger. A piston disk is mounted at the end of the plunger shaft, and hand operation of the trigger moves the plunger shaft and piston through the cartridge to urge compound therefrom. In some cases, such dispensing guns are adapted for use with a double cartridge for dispensing two-component chemical systems such as epoxy and hardener. These are twin-barrel epoxy guns have a pair of plunger shafts commonly driven by a manual trigger mechanism. Some of the two-component chemicals such as epoxy/hardener are of different viscosities which create uneven ejection pressures on the ejection pistons. Additionally, some of these materials are very thick and difficult to eject and require considerable pressure.
For example, U.S. Pat. No. 5,104,005 to Schneider, Jr. et al. issued Apr. 14, 1992 discloses a dual-component gun having a high-pressure ratchet assembly. Also of interest is U.S. Pat. No. 3,767,085 to Cannon et al. which shows a double barrel syringe having a common mixing chamber. Received in the barrels are cartridges containing the two constituents to be mixed, each cartridge having a rear plug which is engaged by a piston. The dual piston rods are urged axially inwardly so that pistons 71 and 72 (FIG. 1 therein) are urged their full distance through the cartridges.
It is greatly advantageous if these dual-cartridge type guns can accommodate a range of the various-sized dual-compound cartridges that are now available. Otherwise, it would be necessary to purchase multiple guns, one for each cartridge size. A helpful feature in this latter regard is shown in U.S. Pat. No. 5,197,635 to the inventor herein and issued on Mar. 30, 1993. The '635 patent discloses a snap-on piston assembly provided at the ends of the dual plunger shafts (see FIG. 9 therein). The snap-on piston assembly 450 includes a piston 455, and a hollow cylindrical base 460 on which piston 455 is mounted. When a plunger shaft is fully inserted within base 460, a detent ball-bearing 510 releasibly locks it onto the end of the plunger shaft. Many shapes and sizes of pistons 455 may be easily interchanged with this assembly in order to accommodate the various twin epoxy cartridges now available.
While the above-described snap-on piston assembly 450 helps to accommodate different sized cartridges, it also creates a need to secure the various dual cartridges in place despite fixed-size barrels. Often, odd-sized cartridges are used and these must be centered and secured regardless of their size. Otherwise, the cartridges may become loose or uneven and this will cause one side of the tube to extrude more material than the other side. With epoxy or any other two-part compound, the mix ratio is of utmost importance. Centering the cartridges also helps to prevent blowback, a problem of compound extruding rearwardly which in most cases destroys the cartridge and wastes expensive compound. One known attempt at a solution is a spring-biased centering disk that rides the plunger shaft behind the piston. Once the pistons are inserted into the cartridges, the centering disk behind each piston is spring-biased into the rear apertures of the cartridges to thereby keep them centered relative to the plunger shafts. These centering disks are commercially available on certain dispensing guns such as the Cox model PPM-300. Unfortunately, for each piston size, a different centering disk must be kept on hand. In addition, each time a cartridge is exchanged for one of a different size, a different-sized centering disk must be assembled onto the plunger shaft, and this is a tedious and time-consuming process.
It would be greatly advantageous to provide a means for securing and centering various sized cartridges without ever having to touch, adjust, change or remove the centering components for any reason.